.center {
          margin: auto;
          width: 60%;
          border: 3px solid #73ad21;
          padding: 10px;
          font-family: Arial, Helvetica, sans-serif;
        }
        a:link {
          background-color: yellow;
          text-decoration: none;
        }

        a:visited {
          background-color: cyan;
        }

        a:hover {
          background-color: lightgreen;
        }

        a:active {
          background-color: hotpink;
        }
        footer {
          text-align: center;
        }